Shadow mask support means for a color television image tube

ABSTRACT

In a shadow mask support means comprising a bi-metal piece having one end secured to a shadow mask frame with the other end left free, and a leaf spring secured at one end to said free end of the bi-metal piece and extending therefrom toward a pin provided on a side wall of a face panel, the improvement residing in that a metallic plate portion disposed between said frame and said spring is so arranged that it is displaced due to thermal deflection of the bi-metal at the end adjacent to said pin by an amount smaller than the displacement at the opposite end.

United States Patent Nakamura et al.

[ 51 May2,1972

Dol. Kobe; Aklra Sato, Takatsuki; Yushln Suzlki, Amagasaki. all of Japan[73] Assignee: Mataushita Electronics Corporation,

Osaka, Japan [22] Filed: Mar. 16, 1970 [21] Appl. No.: 19,945

[30] Foreign Application Priority Data Mar. 19, 1969 Japan ..44/2l834Mar. 19, 1969 Japan ..44/2l833 [52] U.S. Cl. ..3l3/85 S, 313/292 [5l]Int. Cl ..l-l0lj 29/06, HOlj 29/02, H0lj 31/20 [58] Field of Search ..31 3/92 B, 85 S (56] References Clted UNITED STATES PATENTS 3,449,6l l6/1969 Schwartz et al "313/85 S Primary Examiner-Robert SegalAu0rneyStevens, Davis, Miller & Mosher ABSTRACT In a shadow mask supportmeans comprising a bi-metal piece having one end secured to a shadowmask frame with the other end left free, and a leaf spring secured atone end to said free end of the bi-metal piece and extending therefromtoward a pin provided on a side wall of a face panel, the improvementresiding in that a metallic plate portion disposed between said frameand said spring is so arranged that it is displaced due to thermaldeflection of the bi-metal at the end adjacent to said pin by an amountsmaller than the displacement at the opposite end.

2 Claims, 7 Drawing Figures Patented May 2, 1972 3,660,708

2 Sheets-Sheet 1 FIG. I PRIOR ART #M/(Mmq K 100/,

A J? m 9M0 X 302 0/0 INVENTOR ATTORNEYS hunt! M- 2,1912 3,660,708

' z sham-shut a SHADOW MASK SUPPORT MEANS FOR A COLOR TELEVISION IMAGETUBE The present invention relates to a mechanismfor supporting theshadow mask of a color television picture tube at three or four placesin its frame on a face panel.

In a picture tube provided with a shadow mask, the shadow mask isnormally supported resiliently on a face panel through mask supportersat three or four places on the mask frame itself. For said masksupporter, a metallic leaf spring is generally used. This spring iswelded at one of its ends to the outer face of the frame side wall, theother end of said spring being engaged by a pin provided on the innersurface of the side wall of the face panel through a hole formed on saidother end of the leaf spring.

However, in such a mask support mechanism, when thermal expansion occursin the shadow mask during operation of the picture tube, the electronbeam path is deviated with the result that the color puritycharacteristics of the picture tube are substantially degraded.

In order to overcome this disadvantage, it has hitherto been proposed toprovide a bi-metal piece in a shadow mask supporter so that the shadowmask is slightly displaced toward the screen in accordance with thethermal expansion of the shadow mask.

However, in this arrangement, when the bi-metal piece is deflected, thespring is subjected to a local twist which undesirably prevents theshadow mask from being uniformly displaced throughout its surface.

Therefore, an object of the present invention is to reduce the amount ofthe twist which appears when the bi-metal is deflected.

It is a further object of the present invention to reduce the relativesliding movement between the spring and said pin at the points ofengagement thereof.

It is a still further object of the present invention to arrange theshadow mask so that it can be displaced smoothly and uniformlythroughout its surface along the axis of the tube when it is thermallyexpanded or contracted.

The present invention will now be described with reference to preferredembodiments shown by way of example in the accompanying drawings, inwhich;

FIG. 1 is a plan view illustrating a conventional mask support mechanismfor a color television picture tube;

FIG. 2 is a perspective view showing a mask supporter which may be usedin the conventional mask support mechanism;

FIG. 3 is a fragmentary perspective view showing the operation of themask supporter shown in FIG. 2; and

FIGS. 4 through 7 show perspective views of various mask supporters,each of which may be used in a mask support mechanism made in accordancewith the present invention.

In a conventional mask support mechanism shown in FIG. 1, a shadow mask1 is mounted within a face panel 3 by means of three mask supporter 4, 5and 6 disposed in a space between a frame 2 of the shadow mask and theface panel 3. All of the mask supporters 4, 5 and 6 are substantiallyidentical in shape; however, these three mask supporters do not act onthe shadow mask 1 symmetrically about the center line of the surface ofthe shadow mask 1.

Further, in a known structure which is shown in FIG. 2 and in which amask supporter is provided with a bi-metal piece, the bi-metal piece 7is rectangular in shape and welded at one end to the outer surface ofthe side wall-of the frame 2. The other end or free end of the bi-metalpiece 7 is welded to one end of a leaf spring 8, the other end of thespring 8 being in turn connected by means of a hole 9 provided thereinto a pin 10 projecting from a side wall of the panel 3. The bi-metalpiece 7 is so arranged that the metallic layer 7a of a lower coefficientof thermal expansion is disposed adjacent to the frame 2 and themetallic layer 7b of a higher coefficient of thermal expansion isdisposed adjacent to the panel 3, whereby the bi-metal piece 7 isdeflected towards the tube axis in response to an increase intemperature. In the drawing, the

reference numeral ll shows a fluorescent screen and 7c the weldingspots.

According to the above described mechanism, when thermal exansion takesplace in the shadow mask 1, for example, during the manufacture or theoperation of the picture tube, the apertures in the shadow mask 1 aredisplaced along the plane of the mask surface from the center thereoftowards its periphery. However, in this instance, the bi-metal piece 7in each of the mask supporters is deflected at its lower portion asshown in FIG. 3. This deflection serves to give the spring 8 a tendencyto shift its outer end which is outwardly extended or the end in whichthe hole 9 is provided downwardly as seen in the drawing with respect tothe shadow mask 1. Since the hole 9 is in engagement with the pin 10,the shadow mask 1 is in ef fect displaced towards the screen 11 so thatthe path of the electron beam is substantially free from deviation,despite the fact that the apertures are displaced as described above. Inother words, the apertures of the shadow mask 1 are shifted along apredetermined electron beam path.

However, in this known structure, since the bi-metal piece 7 serves todeflect the spring 8 uniformly throughout the welded edge 12 thereof andsince there exists a substantial frictional resistance between the hole9 of the spring 8 and the pin 9, the spring 8 is subjected, when thebi-metal piece 7 is deflected, to a local twist at the portion betweenthe point 13 and the hole 9. Since a few, for example three, of suchmask supporters are disposed asymmetrically as shown in FIG. 1, it isdifficult to uniformly maintain the displacement of the shadow mask 1for compensating the thermal expansion thereof throughout its surface,and there often appears a non-uniform displacement of the shadow maskcausing an uneven compensation effect. Particularly, a mask supporterdisposed on the upper periphery of a rectangular panel will cause adisplacement of the shadow mask which is asymmetrical about its verticalcenter line.

Further, in this known structure, the spring 8 or the frame 2 will bepossibly subjected to a permanent deformation during the hightemperature treatment which may be performed during the manufacture ofthe picture tube.

The present invention has been accomplished to eliminate the abovedescribed disadvantages of the known arrangement and aims to provide anarrangement in which a metallic plate portion disposed between the frame2 and the spring 8 is thermally displaced by means of a bi-metal at theside adjacent to the pin 10 by an amount smaller than that at theopposite side.

The present invention will now be described in more detail withreference to the accompanying drawings. Referring to FIG. 4, a bi-metalpiece is designated by a reference numeral 17. As will be seen in thedrawing, the bi-metal piece 17 is welded to the frame 2 along a weldingline L of which extension intersects, at an angle 0 degree, theextension of a welding line I at points on which line the bi-metal piece17 is welded to the spring 8. The angle 6 may be selected to have anydesired value within a range from 5 to 40, however, an angle of about 15is preferred. The bi-metal piece 17 is trapezoidal in shape and has ametallic layer 17a of a lower coefficient of thermal expansion facingtoward the frame 2 and another metallic layer 17b of a highercoefficient of thermal expansion facing towards the side wall of thepanel 3.

Three or four of such mask supporters may be used. In the former case,the supporters may be disposed as shown in FIG. 1 and, in the lattercase, they may be disposed one at each of the sides.

According to the mask supporter shown in FIG. 4, the portion of thebi-metal located between the frame 2 and the spring 8 is in effectthermally displaced at the side 13' adjacent to the pin 10 by a smalleramount than at the opposite side 14' whereby the spring 8 is twisteduniformly in the same direction throughout its length. Further, in thesupport mechanism using such mask supporters, one of the mask supportersis free from irregular influence of the other supporters, so that theframe 2 and the shadow mask 1 can be smoothly displaced along the tubeaxis in accordance with the deflection of the bi-metal piece 17, and thedeflection of the shadow mask 1 is uniform throughout the mask surface.Further, in accordance with the above-described arrangement, the problemof permanent deformation as well as the trouble of the detachment ofwelded spots, which may be encountered in the vconventional structure,can be safely eliminated.

A further embodiment of the present invention is shown in FIG. 5. Inthis embodiment, two bi-metal pieces 27 and 37 are employed in parallelfor one mask supporter, the thermal deflection of the bi-metal piece 37adjacent to the pin being determined to be smaller as compared with thatof the other bi-metal piece 27. This is done by determining thecombination of the materials for the lower thermal expansion metal layer270 and the higher thermal expansion metal layer 27b to be differentfrom that of the materials for the lower thermal expansion metal layer37a and the higher thermal expansion metal layer 37b so that thedeflections of the bi-metal pieces 27 and 37 are different from eachother. Alternatively, the thickness or shapes of the layers may bevaried to accomplish the same purpose. Further, the bi-metal piece 37located at the side adjacent to the pin may be replaced by a metal platehaving a single layer.

in the embodiment of the present invention shown in FIG. 6, a U-shapedmetal plate 47a of a lower thermal expansion coefficient is combinedwith a metal plate 47b of a higher thermal expansion coefficientattached thereto at its leg remote from the pin, the other leg of theplate 47a being left as a single layer metal plate.

Further, in the embodiment shown in FIG. 7, a substantially rectangularbi-metal piece 57 having a metal plate 570 of a lower thermal expansioncoefficient and a second metal plate 57b of a higher thermal expansioncoefficient is further combined with a small metal piece 57;- welded tothe outer side surface of the metal plate 57b at the side nearer to thepin so that the amount of deflection of the bi-metal is mechanicallyreduced at this side.

It is to be noted that a shadow mask mechanism should not necessarily beprovided with the mask supporter of the present invention in all of thelocations where mask supporters are used, but only one of the tubesupporter of the present invention may be used at the upper side of theface panel and two or three mask supporters having conventional bi-metalarrangements may be used in the other places.

What is claimed is:

1. A shadow mask support mechanism for a color television picture tubeincluding a plurality of mask supporters for supporting a shadow maskspread out on a frame opposite a face panel, at least one of said masksupporters comprising a bimetallic element having metal layers ofdifferent thermal coefficients of expansion for the deformation of saidbimetallic element upon its heating for the purpose of displacing saidshadow mask in the direction of the television screen, said bimetallicelement being positioned in the direction of the length of said tube andsecured at its one end to said shadow mask frame and at the other freeend to one end of a leaf spring, the other end of said leaf springextending in the direction of and engaging a pin secured on the sidewall of said face panel, wherein said bimetallic element is disposedsuch that its free end on the side thereof closer to said pin thermallydeforms less than on the side thereof disposed away from said pin, saidbimetallic element being welded to said frame along a line intersectinga line along which said bimetallic element is welded to said spring, theangle of intersection of said welding lines being between approximately5 and 40.

2. A shadow mask support mechanism in accordance with claim 1, in whichsaid angle of intersection is substantially 15.

1. A shadow mask support mechanism for a color television picture tubeincluding a plurality of mask supporters for supporting a shadow maskspread out on a frame opposite a face panel, at least one of said masksupporters comprising a bimetallic element having metal layers ofdifferent thermal coefficients of expansion for the deformation of saidbimetallic element upon its heating for the purpose of displacing saidshadow mask in the direction of the television screen, said bimetallicelement being positioned in the direction of the length of said tube andsecured at its one end to said shadow mask frame and at the other freeend to one end of a leaf spring, the other end of said leaf springextending in the direction of and engaging a pin secured on the sidewall of said face panel, wherein said bimetallic element is disposedsuch that its free end on the side thereof closer to said pin thermallydeforms less than on the side thereof disposed away from said pin, saidbimetallic element being welded to said frame along a line intersectinga line along which said bimetallic element is welded to said spring, theangle of intersection of said welding lines being between approximately5* and 40* .
 2. A shadow mask support mechanism in accordance with claim1, in which said angle of intersection is substantially 15* .